T cell recognition of the posttranslationally cleaved intersubunit region of influenza virus hemagglutinin.

The influenza virus hemagglutinin is synthesized as a single polypeptide chain, but upon maturation it will posttranslationally be modified by a host cell related trypsin-like enzyme. The enzymatic cleavage attacks the so-called intersubunit region of the molecule giving rise to covalently linked HA1 and HA2 subunits. An I-Ed-restricted T cell epitope was identified in the highly conserved intact intersubunit region of the influenza virus hemagglutinin. T cell recognition of a 25-mer synthetic peptide comprising the intact intersubunit region does not require further processing and the elimination of the intervening Arg residue coupling the fusion peptide to the C-terminal segment of HA1 does not abolish the T cell activating capacity. The fine specificity pattern of a T cell hybridoma similar to that of the polyclonal T cell response demonstrates that a single T cell receptor is able to recognize peptides of different sizes representing not only the uncleaved but also the cleaved form of this hemagglutinin region. Based on specificity studies the epitope was localized to the C-terminal 11 amino acids of the HA1 subunit. The cross-reactivity of peptide-primed T cells with influenza virus infected antigen-presenting cells shows that fragments comprising the identified epitope of the intersubunit region can be generated as a result of natural processing of the hemagglutinin molecule. As antigen-presenting cells are lacking the enzyme which is responsible for the posttranslational modification of newly synthesized hemagglutinin molecules, the role of immature viral proteins in immune recognition is discussed.

Identification of the plasmid and the structural gene of colicin type 7 of Shigella sonnei.

Shigella sonnei colicin 7 (Scol7) is a unique bacteriocin acting only on certain dysentery-causing bacteria, like enteroinvasive Escherichia coli, S. sonnei or S. boydii. We identified a 4.2 Md plasmid (pScol7) conferring Scol7 production to the transformants. The entire plasmid was sequenced (Gene Bank Accession number AJ318075) and the structure gene of Scol7 production (sc7a) was identified. Analyzing the sequence of the plasmid revealed extensive homology to other colicin plasmids, particularly to pColE1 but only in areas not related to the bacteriocin activity gene. The similarity of the putative promoter for sc7a to the respective sequences of other colicins suggested that the production of Scol7 is under SOS regulation. Indeed, its production could be increased eightfold by mitomycin C treatment. The molecular mass of the translated polypeptide as deduced from the nucleotide sequence of sc7a (i.e. 11.2 kDa) is in good agreement with previous estimations for its subunit, but molecular filtration experiments suggest a multimeric structure of at least 50 kDa. While current data are not sufficient to predict the mode of action of Scol7, the presence of a DTLSN pentapeptide motive suggests that it could be imported to sensitive cells via the TonB transport system.

Topo-optical investigations on the surface of bacterial cells during the phagocytosis of Klebsiella pneumoniae in mouse.

Polarisation optical methods provide the means to perform sub-microscopic investigations on structures containing spatially highly ordered molecules, for example the cell envelope of prokaryotic cells. Such structures can evoke birefringence, which can be enhanced or modified by different dyes or reagents, thus providing the possibility of a more specific investigation of the composition and structure of bacterial surface compounds. Klebsiella pneumoniae synthesises sterically different carbohydrate-rich structures, including those of the outermost capsular polysaccharide, the polysaccharide somatic antigen of the lipopolysaccharide molecule and the peptidoglycan layer of the cell wall. In the study reported here, the nature and intensity of topo-optical activity of these structures was analysed using the aldehyde-bisulphite-toluidine blue reaction, sialic acid topo-optical reactions and chlorpromazine-eosin charge transfer reactions. Furthermore, a mouse intraperitoneal model was used to analyse alterations in topo-optical characteristics of bacteria during phagocytosis. Both encapsulated and non-encapsulated bacterial cells changed their original pattern and orientation of birefringence after being phagocytosed.

Polarization optical analysis of the surface structures of various fungi.

Vicinal hydroxyl groups of the sugar compounds sialic acid and 9-O-acyl sialic acid can be visualised for polarization optical analysis on the surface of different fungi using several topo-optical reactions. We investigated the presence of these molecules in cultures of Cryptococcus neoformans (heterogeneous form), Saccharomyces cerevisiae, Candida albicans, Candida glabrata, Candida krusei and Candida tropicalis by topo-optical reactions. Additionally, we examined brain and stomach tissues of patients with infections by C. neoformans and C. albicans, respectively. The results suggest a highly fashioned orientation of the sugar chains on the fungal surface. Terminal sialic- and O-acyl sialic acid residues are permanently present and orientated in a highly specific way in the cell wall of fungi. Based on the polarization optical analysis after the ABT-r (anisotropic PAS-r), the linear oriented hydroxyl groups of the sugar molecules are localized either perpendicular or parallel to the surface coat, depending on the species. According to the orientation of the vicinal hydroxyl groups, the oligosaccharide chains are orientated vertically. The capsule of the heterogeneous form of C. neoformans presented an especially strong metachromatic reaction and anisotropy. It is especially remarkable that the sterical orientation of sugar chains, and the terminal sialic acid and 9-O-acyl sialic acid molecules, was opposite in the inner and outer layer of the capsule.

Laminin binding to Prevotella intermedia.

The interaction of laminin (Lm), a basement membrane protein abundant in the periodontium, with 66 strains of Prevotella intermedia isolated from diseased pockets, was tested in a 125I-labeled protein binding assay. The mean binding value was 28% of the total protein added. The binding significantly increased to 35% when the environmental pH decreased from 7 to 6. The Lm interaction was characterized in a highly binding (about 65%) strain, OMGS105. The binding was rapid and required about 1 min and 1-2 h for 50% and 100% equilibrium respectively. The 125I-Lm binding was maximum in the pH interval 3.0 to 6.5 and could not be displaced by unlabeled Lm or inhibited by other proteins and carbohydrates. The interaction was stable in the presence of NaCl or urea (concentrations up to 4 M) but was dissociated by > or = 1 M KSCN. The Lm-binding component was thermolabile and sensitive to proteolytic enzymes. Sodium dodecylsulfate-polyacrylamide gel electrophoresis and Western blot analysis revealed a approximately 62 kDa Lm-binding protein, both in the whole cell extract and the outer membrane preparation. Weaker binding was also observed to other proteins. These data establish the ability of P. intermedia to interact with Lm via certain cell surface proteins, a property that might contribute to the colonization of this bacterium in the periodontal pocket.

Lactoferrin-binding proteins in Shigella flexneri.

The ability of Shigella flexneri to interact with lactoferrin (Lf) was examined with a 125I-labeled protein-binding assay. The percent binding of human lactoferrin (HLf) and bovine lactoferrin (BLf) to 45 S. flexneri strains was 19 +/- 3 and 21 +/- 3 (mean +/- standard error of the mean), respectively. 125I-labeled HLf and BLf binding to strain M90T reached an equilibrium within 2 h. Unlabeled HLf and BLf displaced the 125I-HLf-bacteria interaction in a dose-dependent manner. The Lf-bacterium complex was uncoupled by KSCN or urea, but not by NaCl. The interaction was specific, and approximately 4,800 HLf binding sites (affinity constant [Ka], 690 nM) or approximately 5,700 BLf binding sites (Ka, 104 nM) per cell were estimated in strain M90T by a Scatchard plot analysis. The native cell envelope (CE) and outer membrane (OM) did not reveal Lf-binding components in sodium dodecyl sulfate-polyacrylamide gel electrophoresis. However, after being boiled, the CE and OM preparations showed three distinct horseradish peroxidase-Lf reactive bands of about 39, 22, and 16 kDa. The 39-kDa component was also reactive to a monoclonal antibody specific for porin (PoI) proteins of members of the family Enterobacteriaceae. The Lf-binding protein pattern was similar with BLf or HLf, for Crb+ and Crb- strains. The protein-Lf complex was dissociable by KSCN or urea and was stable after treatment with NaCl. Variation (loss) in the O chain of lipopolysaccharide (LPS) markedly enhanced the Lf-binding capacity in the isogenic rough strain SFL1070-15 compared with its smooth parent strain, SFL1070. These data establish that Lf binds to specific components in the bacterial OM; the heat-modifiable, anti-PoI-reactive, and LPS-associated properties suggested that the Lf-binding proteins are porins in S. flexneri.